Recently, as electronic devices become smaller and lighter, batteries used therein as power sources are increasingly required to have a compact size and light weight. As rechargeable batteries with a compact size, light weight and high capacity, lithium secondary batteries have been put to practical use and widely used in portable electronic and communication devices such as compact camcorders, portable phones, notebook PCs, or the like.
A lithium secondary battery comprises a cathode, an anode and an electrolyte. Such lithium secondary batteries are capable of repeated charge/discharge cycles, because lithium ions deintercalated from a cathode active material upon the first charge cycle are intercalated into an anode active material (for example, carbon particles) and deintercalated again during a discharge cycle, so that lithium ions reciprocate between both electrodes while transferring energy.
In general, metals and metal alloys, such as iron, aluminum, copper, nickel, etc. are widely used as materials for forming a can for housing a lithium secondary battery and forming a collector of a lithium secondary battery. Such metallic materials are not susceptible to corrosion (oxidation) under the normal charge/discharge conditions of a lithium secondary battery. However, under extreme conditions, such as overcharge, overdischarge and high-temperature storage conditions, such metallic materials tend to show a great possibility of corrosion. Particularly, when a battery is overdischarged to a voltage of 0V at low current or under constant resistance, the voltage of an anode having a high irreversible capacity increases in advance of the voltage of a cathode. Under these circumstances, when the anode voltage reaches to a specific voltage range of about 3.6V or higher, at which point copper foil used as an anode collector is oxidized, copper dissolution (i.e. oxidation) occurs, resulting in damages of the battery. In brief, corrosion of metallic materials present inside of a battery under the overcharge, overdischarge and high-temperature storage conditions, causes the problems of self-discharge, a drop in capacity, internal short circuit and an increase in internal resistance of the battery, resulting in degradation in the quality of a battery and damages of the battery.